A great deal of diagnostic procedures and laboratory research are carried out wherein deoxyribonuveic acid (DNA), ribonuveic acid (RNA) or proteins are separated according to their physical and chemical properties via electrophoresis. This process is widely used and has many applications. For example, it is used to analyze DNA molecules according to their resultant size after being digested by restriction enzymes. It is also used to analyze the products of a polymerase chain reaction (PCR).
Typically, electrophoresis separation is carried out in a separation medium, such as a gel of agarose or acrylamide or a combination of the two. Usually, agarose gels are cast in open trays and form a slab whereas acrylamide gels are cast between two glass plates.
In order to effect the electrophoretic separation, two opposite ends of the gels are exposed to an electrically conducting buffer which is connected by electrodes, typically carbon or platinum, to an electric power source. Once the electrical power source is switched on, the electric field forces negatively charged molecules to move towards the anode and positively charged molecules to move towards the cathode. One characteristic of conventional electrophoresis is the use of large volumes of buffer having a relatively low salt concentration to maintain the required electric field.
DNA is negatively charged and therefore, in the agarose or acrylamide gels which provide sieving action, DNA molecules move towards the anode at a rate which depends on their size, wherein the smaller the molecules the faster they move.
Typically, it is desirable to visualize and to document the results of the electrophoretic separation test. In electrophoretic separation of DNA molecules, this has been done by immersing the gel slab after the electrophoretic separation has been completed in a solution of a fluorescent compound which emits visible light when exposed to a ultra violet (UV) light. A widely used compound is ethidium bromide.
Conventional electrophoretic separation systems are deficient in many respects, a few of which are listed below.
Prior art electrophoresis separation systems are a potential source of contamination to the working environment in which the tests are performed. The two major sources of contamination are ethidium bromide and PCR products. Ethidium bromide is a hazardous chemical due to its mutagenic activity and therefore, exposure to ethidium bromide may induce malignant tumors. PCR is an extremely sensitive method to the extent that a single molecule of DNA product from one PCR (out of the trillions of molecules being produced) may interfere with the subsequent PCR such that it will produce incorrect result.
Conventional electrophoresis is also deficient in other respects, one being that it is time consuming.
Various attempts have been made to solve the deficiencies of conventional electrophoresis. Most attempts have been addressed to overcome the deficiency of conventional electrophoresis systems with respect to the use of buffers therein.
U.S. Pat. No. 4,874,491 to Stalberg describes an electrophoresis system having a high concentration buffer containing gel.
U.S. Pat. No. 4,892,639 to Sarrine et al. describes an electrophoresis plate with improved buffer circulation.
U.S. Pat. No. 5,045,164 to Tansamrit et al. describes an electrophoresis plate having thickened ends as buffer reservoirs.
U.S. Pat. No. 5,209,831 to MacConnel describes a bufferless disposable cassette having open ends and conductive film electrodes.